1. Field of the Invention
The present invention relates to ink jet printers, and, more particularly, to a platen for an ink jet printer.
2. Description of the Related Art
An ink jet printer generally includes a platen for supporting a sheet of print medium, such as paper, while an ink jetting printhead deposits ink on the print medium. Beyond merely supporting the print medium, the platen serves to establish and maintain a fixed gap between the printhead and the print medium in order to maximize the printing quality. That is, the platen ensures that the height of the gap between the printhead and the print medium is constant across the width of the platen. The platen includes an outer flat surface, opposing the printhead, upon which the print medium may rest or be biased against.
It is known to form a platen of a single continuous piece of molded plastic. With ink jet printers that print with a resolution of 300 dots per inch (dpi) or 600 dots per inch, the flatness tolerances on the outer surface of the platen which can be achieved through plastic molding are tight enough to produce an acceptable print quality. With high resolution ink jet printers (1200 dpi and greater), however, the flatness tolerance of the outer surface of the platen is a limiting factor of the print quality. That is, the print quality that is achieved with a high resolution ink jet printer can be limited by the flatness of the plastic molded platen. The main cause of the lack of flatness is that the flexibility of the plastic allows it to bend or warp in one direction or another along the width of the platen. Although it is possible to machine a platen to the flatness required by high resolution ink jet printing, the costs associated with such machining are very high.
What is needed in the art is a platen which can be inexpensively manufactured with a flatness tolerance that is tighter than what can be achieved with conventional plastic molding alone.
The present invention provides a plastic platen which is biased by a precision ground metal shaft attached thereto such that the outer surface of the platen has a flatness tolerance which is tighter than what can be achieved with conventional plastic molding alone.
The invention comprises, in one form thereof, an ink jet printer for jetting ink onto a section of a front side of a print medium. The ink jet printer includes an ink jetting printhead facing the front side of the print medium. A media support apparatus opposes the printhead. The media support apparatus includes a substantially flexible body having an outer surface engaging a back side of the print medium such that the section of the print medium receiving the ink is substantially flat. A substantially rigid elongate element engages the body and has a length direction substantially perpendicular to a feed direction of the print medium. The elongate element provides at least a portion of the outer surface of the body with a predetermined degree of straightness.
An advantage of the present invention is that the platen can hold the paper it supports within a flatness tolerance that is tighter than can be achieved by conventional platens.
Another advantage is that it is much less expensive to grind the metal shaft of the present invention to the required straightness than to machine an entire platen to the required straightness.
Yet another advantage is that the platen can be manufactured with minimal assembly time.